(1) Field of the Invention
The present invention relates to an audio-video output apparatus, an authentication processing method, and an audio-video processing system, and particularly to an audio-video output apparatus which outputs at least one of audio data and video data to a receiving apparatus using High Definition Multimedia Interface (HDMI) communications.
(2) Description of the Related Art
In recent years, with advances in high-quality picture technologies and digitalization, HDMI communications which allow high speed digital transmission in an uncompressed mode is used for sending content including audio data and video data from a sending apparatus, such as a DVD recorder or a DVD player, to a receiving apparatus, such as a TV set or an amplifier. Moreover, for the purpose of protecting copyright of the content sent from the sending apparatus, apparatus authentication and content protection defined by the High-bandwidth Digital Content Protection (HDCP) standard (non-patent reference: “HDCP Specification Revision 1.2” of Digital Content Protection, LLC <URL: http://www.digital-cp.com/home>) are used these days.
The HDCP standard is designed to protect transmission of content between a sending apparatus that encrypts and sends content and a receiving apparatus that receives and decrypts the content. According to the HDCP standard, the sending apparatus uses an authentication protocol in order to perform apparatus authentication to verify the receiving apparatus. The apparatus authentication includes multiple authentications, including first, second, and third authentications. When it is judged that the receiving apparatus is an authorized apparatus as a result of the apparatus authentication, the receiving apparatus is allowed to decrypt the content which has been encrypted by the sending apparatus.
The apparatus authentication based on the HDCP standard is performed using Display Data Channel (DDC) communications.
The HDCP standard also defines a processing method, whereby apparatus verification is made as to whether or not the receiving apparatus is an authorized apparatus using an unauthorized apparatus list that includes information regarding unauthorized apparatuses. This list is referred to as the “Vector Revocation List” hereafter in the present specification. The apparatus verification is conducted by checking the validity of “System Renewability Message”, and is executed during first and second authentications. When the receiving apparatus is judged to be an unauthorized apparatus, a process is followed so that the unauthorized receiving apparatus becomes unable to correctly decrypt the content which is currently being received or that the sending apparatus stops sending the content to the unauthorized apparatus, for example.
FIG. 1 is a diagram showing a configuration of a conventional audio-video communication system whereby the apparatus authentication is performed according to the HDCP standard. An audio-video communication system 500 shown in FIG. 1 is an HDMI communication system which includes a sending apparatus 510 such as a DVD player, and a receiving apparatus 520 such as a TV set. The sending apparatus 510 and the receiving apparatus 520 are connected via an HDMI cable 530.
The sending apparatus 510 is an audio-video output apparatus which outputs audio data and video data to the receiving apparatus 520 using the HDMI communications. The sending apparatus 510 includes a CPU (Central Processing Unit) 511, a disk controlling unit 512 for controlling a disk drive, a memory area 513, and an HDMI sending unit 514. The HDMI sending unit 514 is an LSI (Large-Scale Integration) which sends content including audio data and video data to the receiving apparatus 520. More specifically, the HDMI sending unit 514 sends the content including the audio and video data unidirectionally to the receiving apparatus 520 via the HDMI cable 530. The HDMI sending unit 514 has: an authenticating unit 515 for performing the apparatus authentication on the receiving unit 520; an encrypting unit 516 for encrypting the content which is to be sent; and a DDC unit 517. The CPU 511 controls the disk controlling unit 512, the memory area 513, and the HDMI sending unit 514. The DDC unit 517 establishes bidirectional DDC communications with the receiving apparatus 520 via the HDMI cable 530.
The memory area 513 holds the Vector Revocation List which includes information regarding unauthorized apparatuses. Under the assumption that the number of unauthorized apparatuses will be increasing on the market in the future, a latest Vector Revocation List is formed and distributed as appropriate. The sending apparatus 510 can acquire the latest Vector Revocation List through an external recording medium, such as a playback medium, or through a network, such as the Internet. It should be noted here that a method to update the Vector Revocation List is defined by the HDCP standard. After the acquisition of the latest Vector Revocation List through the playback medium or the like, the sending apparatus 510 stores the latest List in the memory area 513 and needs to immediately perform the apparatus verification on the receiving apparatus 520.
The receiving apparatus 520 includes a CPU 521 and an HDMI receiving unit 522. The HDMI receiving unit 522 is an LSI which receives the content including the audio and video data sent from the sending apparatus 510. The HDMI receiving unit 522 has: an authenticating unit 523 for performing the apparatus authentication; and a decrypting unit 524 for decrypting the received content. The CPU 521 controls the HDMI receiving unit 522.
FIG. 2 is a flowchart showing a process flow of the apparatus authentication performed by the conventional audio-video communication system 500. The sending apparatus 510 sets the content on mute, and then starts sending the content to the receiving unit 520 (S501). Here, since the content is set on mute, no picture is displayed and no audio is heard on the receiving apparatus 520. Next, the sending apparatus 510 executes the first authentication in relation to the receiving apparatus 520 (S502).
FIG. 3 is a flowchart showing a flow of the first authentication process (S502) performed by the conventional audio-video communication system 500. For the first authentication process (S502), the authenticating unit 515 first has the sending apparatus 510 and the receiving apparatus 520 exchange information needed for the authentication. In doing so, the sending apparatus 510 acquires Bksv information as the information about the receiving apparatus 520 (S601). The acquired information about the receiving apparatus 520 is held in the memory area 513. After the completion of the information exchange, the sending apparatus 510 and the receiving apparatus 520 generate information needed for the first authentication on the basis of the acquired information. Then, the first authentication process is performed using the generated information (S602). When the first authentication ends abnormally (NG in S602), the information about the receiving apparatus 520 held in the memory area 513 is abandoned (S606). Accordingly, the sending apparatus 510 abnormally ends the authentication process.
When the first authentication normally ends (Pass in S602), the authenticating unit 515 performs the apparatus verification by verifying a signature included in the Vector Revocation List held in the memory area 513 (S603). Next, the authenticating unit 515 judges whether or not the acquired information about the receiving apparatus 520 is present in the Vector Revocation List (S604). When the acquired information about the receiving apparatus 520 is present in the Vector Revocation List (Yes in S604), the authenticating unit 515 judges that the receiving apparatus 520 is an unauthorized apparatus (S605), abandons the information about the receiving apparatus 520 that is held in the memory area 513 (S606), and abnormally ends the authentication process. On the other hand, when the acquired information about the receiving apparatus 520 is not present in the Vector Revocation List (No in S604), the authenticating unit 515 judges that the receiving apparatus 520 is an authorized apparatus (S607). It should be noted here that the first authentication process may be executed after the verification process performed using the Vector Revocation List, that is, S602 may be executed after S607.
When the first authentication is unsuccessful (NG in S502), the sending apparatus 510 abnormally ends the content transmission. When the first authentication is successful (Pass in S502), the mute setting for the to-be-sent content is cancelled (S503). This means that the audio and video data of the content is heard and displayed on the receiving apparatus 520. After this, the authenticating unit 515 judges whether or not the second authentication is necessary (S504). To be more specific, when the receiving apparatus 520 connected to the sending apparatus 510 is further connected to another receiving apparatus, the authenticating unit 515 judges that the second authentication is necessary (Yes in S504). When only one receiving apparatus (i.e., the receiving apparatus 520 in this case) is connected to the sending apparatus 510, the authenticating unit 515 judges that the second authentication is unnecessary (No in S504).
When it is judged that the second authentication is necessary (Yes in S504), the authenticating unit 515 performs the second authentication (S505). It should be noted that a process flow of the second authentication is almost the same as that of the first authentication. A difference is that instead of acquiring the Bksv information in S601, the authenticating unit 515 acquires KSV List information as the information about the other receiving apparatus or apparatuses. Then, in S602, the authenticating unit 515 performs the second authentication instead of the first authentication. Note that the first and second authentications referred to here are the ones defined by the HDCP standard. When the second authentication is unsuccessful (NG in S505), the sending apparatus 510 abnormally ends the content transmission.
Meanwhile, when it is judged that the second authentication is unnecessary (No in S504) or when the second authentication is successful (Pass in S505), the authenticating unit 515 performs the third authentication (S506). Here, the third authentication includes a process to update an encryption key used by the encrypting unit 516 for encryption. When the third authentication is unsuccessful (NG in S506), the sending apparatus 510 abnormally ends the content transmission.
When the third authentication is successful (Pass in S506), the sending apparatus 510 acquires the Vector Revocation List held in the playback medium (S507). When the acquired Vector Revocation List is newer than the one held in the memory area 513 (Yes in S508), the sending apparatus 510 updates the Vector Revocation List held in the memory area 513 (S509). After the Vector Revocation List is updated (S509), the process from S501 to S508 is executed again.
On the other hand, when the acquired Vector Revocation List is older than the one held in the memory area 513 (No in S508), the Vector Revocation List held in the memory area 513 is not updated. Then, the third authentication (S506) is performed at predetermined intervals until the completion of the content transmission (Yes in S510).
According to the process described so far, the conventional sending apparatus 510 performs the apparatus authentication including the first and second authentications using the latest Vector Revocation List, which is updated as needed through the playback medium or the like.
After updating the Vector Revocation List (S509), however, the conventional sending apparatus 510 has to once again perform the first and second authentications (S502 and S505) using the updated Vector Revocation List. It should be noted here that the HDCP standard does not clearly define the apparatus verification performed after the start of the third authentication (S506), this third authentication being performed in a state where the receiving apparatus 520 is currently decrypting the encrypted content sent from the sending apparatus 510 and reproducing the audio and video data of the content. When the first and second authentications are executed once again in this state, the screen would have a temporary “blackout”, meaning that the audio and video are set on mute. This would cause a user to have an extremely annoying situation. Moreover, a length of time of the blackout largely depends on the system configuration and the connection configuration of the HDMI apparatuses. In some cases, the blackout may last for several seconds.
In view of the stated problem, the object of the present invention is to provide an audio-video output apparatus, an authentication processing method, and an audio-video processing system which allow the apparatus authentication process to be performed without causing blackout.